An experiment to induce malignancy or immunity in weanling mice by transplanting skin from irradiated Gross passage A tumor-bearing animals was concluded. No tumors developed at the graft site in any animals. Evidence of immunity was sought by injecting ascites form GPA lymphoma intraperitoneally into the grafted animals. All animals eventually died of disseminated lymphoma. The same protocal will be used on younger recipients in an attempt to induce immunity. A study of the relationship between age and horizontal transmission of GPA lymphoma using skin transplantation techniques was conducted. It was found that weanling animals regularly developed GPA lymphoma when grafted with tumor bearing skin - regardless of age. The length of the latency period however proved to be inversely related to age: The older the animal, the shorter the latency period. A comparative study of the normal and preleukemic thymus potentials for survival was studied. Neonatally thymectomized mice were implanted with either a preleukemic or a normal thymus or left unreconstituted. It was found that initially the preleukemic and normal thymus showed the same capacity of body weight maintenance and survival. Eventually the preleukemic thymus implant mice began to decline. GPA virus lymphoma was ultimately detected in 50% of the preleukemic thymus implanted animals.